Types of screws

AKA Resistorx™. Like a regular Torx but with a pin on the center that prevents a regular bit from entering. A drill table and 3/32" metal drill bit could be used to machine a regular Torx to defeat it. I've been able to remove them with a small slotted screwdriver wedged between the center pin and in two of the torx grooves.

Two half-moons shapes on top of each other, a regular slotted screwdriver grabs on the straight edges to fasten but slips on the sloped side. One-way slotted are used in LOTS of public restrooms --czeano. Evil*.

Oval shaped machine screws

If not recessed, a good pair of pliers can bite on the screw head and remove it.